ترغب بنشر مسار تعليمي؟ اضغط هنا

Relation between width of the zero-bias anomaly and Kondo temperaure in transport measurements through correlated quantum dots: Effect of asymmetric coupling to the leads

81   0   0.0 ( 0 )
 نشر من قبل Diego Perez Daroca
 تاريخ النشر 2018
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

The zero-bias anomaly at low temperatures, originated by the Kondo effect when an electric current flows through a system formed by a spin-$1/2$ quantum dot and two metallic contacts is theoretically investigated. In particular, we compare the width of this anomaly $2T_{rm NE}$ with that of the Kondo resonance in the spectral density of states $2T_{K}^{rho}$, obtained from a Fano fit of the corresponding curves and also with the Kondo temperature, $T_K^G$, defined from the temperature evolution of the equilibrium conductance $G(T)$. In contrast to $T_K^G$ and $2T_{K}^{rho}$, we found that the scale $2T_{rm NE}$ strongly depends on the asymmetry between the couplings of the quantum dot to the leads while the total hybridization is kept constant. While the three scales are of the same order of magnitude, $2T_{rm NE}$ and $T_{K}^{rho}$ agree only in the case of large asymmetry between the different tunneling couplings of the contacts and the quantum dot. On the other hand, for similar couplings, $T_{rm NE}$ becomes larger than $T_{K}^{rho}$, reaching the maximum deviation, of the order of $30%$, for identical couplings. The fact that an additional parameter to $T_{rm NE}$ is needed to characterize the Kondo effect, weakenig the universality properties, points that some caution should be taken in the usual identification in experiments of the low temperature width of the zero-bias anomaly with the Kondo scale. Furthermore, our results indicate that the ratios $T_{rm NE}/T_K^G$ and $T_{K}^{rho}/T_K^G$ depend on the range used for the fitting.

قيم البحث

اقرأ أيضاً

114 - I. Weymann , P. Trocha 2014
The Andreev transport through a quantum dot coupled to two external ferromagnetic leads and one superconducting lead is studied theoretically by means of the real-time diagrammatic technique in the sequential and cotunneling regimes. We show that the tunnel magnetoresistance (TMR) of the Andreev current displays a nontrivial dependence on the bias voltage and the level detuning, and can be described by analytical formulas in the zero temperature limit. The cotunneling processes lead to a strong modification of the TMR, which is most visible in the Coulomb blockade regime. We find a zero-bias anomaly of the Andreev differential conductance in the parallel configuration, which is associated with a nonequilibrium spin accumulation in the dot triggered by Andreev processes.
We study the low temperature properties of the differential response of the current to a temperature gradient at finite voltage in a single level quantum dot including electron-electron interaction, non-symmetric couplings to the leads and non-linear effects. The calculated response is significantly enhanced in setups with large asymmetries between the tunnel couplings. In the investigated range of voltages and temperatures with corresponding energies up to several times the Kondo energy scale, the maximum response is enhanced nearly an order of magnitude with respect to symmetric coupling to the leads.
The transmission of electrons through a non-interacting tight-binding chain with an interacting side quantum dot (QD) is analized. When the Kondo effect develops at the dot the conductance presents a wide minimum, reaching zero at the unitary limit. This result is compared to the opposite behaviour found in an embedded QD. Application of a magnetic field destroys the Kondo effect and the conductance shows pairs of dips separated by the charging energy U. The results are discussed in terms of Fano antiresonances and explain qualitatively recent experimental results.
79 - T. A. Costi 2019
Recent experiments have measured the signatures of the Kondo effect in the zero-field thermopower of strongly correlated quantum dots [Svilans {em et al.,} Phys. Rev. Lett. {bf 121}, 206801 (2018); Dutta {em et al.,} Nano Lett. {bf 19}, 506 (2019)]. They confirm the predicted Kondo-induced sign change in the thermopower, upon increasing the temperature through a gate-voltage dependent value $T_{1}gtrsim T_{rm K}$, where $T_{rm K}$ is the Kondo temperature. Here, we use the numerical renormalization group (NRG) method to investigate the effect of a finite magnetic field $B$ on the thermopower of such quantum dots. We show that, for fields $B$ exceeding a gate-voltage dependent value $B_{0}$, an additional sign change takes place in the Kondo regime at a temperature $T_{0}(Bgeq B_{0})>0$ with $T_0<T_1$. The field $B_{0}$ is comparable to, but larger than, the field $B_{c}$ at which the zero-temperature spectral function splits in a magnetic field. The validity of the NRG results for $B_{0}$ are checked by comparison with asymptotically exact higher-order Fermi-liquid calculations [Oguri {em et al.,} Phys. Rev. B {bf 97}, 035435 (2018)]. Our calculations clarify the field-dependent signatures of the Kondo effect in the thermopower of Kondo-correlated quantum dots and explain the recently measured trends in the $B$-field dependence of the thermoelectric response of such systems [Svilans {em et al.,} Phys. Rev. Lett. {bf 121}, 206801 (2018)].
We calculate the conductance through a single quantum dot coupled to metallic leads, modeled by the spin 1/2 Anderson model. We adopt the finite-U extension of the noncrossing approximation method. Our results are in good agreement with exact numeric al renormalization group results both in the high temperature and in the Kondo (low temperature) regime. Thanks to this approach, we were able to fit fairly well recently reported measurements by S. De Franceschi et al. in a quantum dot device. We show that, contrarily to what previously suggested, the conductance of this particular device can be understood within the spin-1/2 Anderson model, in which the effects of the multilevel structure of the dot are neglected.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا